Effects of microwave and ultrasound pretreatments on enzymolysis of milk protein concentrate with different enzymes

Milk protein concentrate was pretreated either by microwave irradiation or by ultrasound before initiation of 3-h enzymatic hydrolysis. The duration of pretreatment ranged from 1 to 8min at a power level of 800W, with the control not being subjected to any pretreatment, and five enzymes (Alcalase, Trypsin, Neutrase, Alkaline Protease and Flavourzyme) were employed. The effects of microwave and ultrasound pretreatments on the kinetics and degree of hydrolysis, protein solubility, bitterness and angiotensin-converting enzyme inhibitory activity were evaluated. Pretreatments increased the degree of hydrolysis and stabilised the solubility of the hydrolysates but could not significantly reduce bitterness of the hydrolysates The angiotensin-converting enzyme inhibitory activity of the hydrolysates were improved with 5-min ultrasound-pretreated Neutrase hydrolysates giving IC50 value of 0.23mg mL(-1). Kinetic parameters showed improved catalytic efficiencies. Pretreatments of milk protein concentrates with either microwave or ultrasound significantly improve the bioactivity and functional characteristics of the resulting hydrolysates.